THE REHEARSAL for October begins in February, at the dawn of a new season, on a back field where the only audience is a small gaggle of autograph-hunting diehards. The stillness of a bleary-eyed morning is broken only by the crack of a bat.

Long before the postseason, teams imagine how October moments will play out. A hitting coach breaks the monotony of batting practice, calling out game situations—sometimes the most critical ones imaginable. In this case it's John Mabry, barking from behind the batting cage at the Cardinals' complex in Jupiter, Fla.: "Ninth inning, two outs! A hit here, we go to the World Series!"

A machine that fires 80-mph curveballs is rooted to the mound, a base runner stands at second. The hitter digs in and imagines the moment: the bright lights of the postseason, the brain-assaulting roar of the towel-waving faithful, the pitcher staring down from the mound. A game, maybe even a championship, on the line.

A hit, and you're the hero. An out, you're the goat. In October there is no in-between.

CLUTCH HITS, clutch pitches, clutch steals, clutch catches: Baseball's postseason is a series of intense, pressurized moments, the ultimate celebration of small sample sizes after the long haul of the regular season. And few things in sports are more alluring than the idea of a clutch gene—the notion that some athletes are wired differently, with an innate ability to perform their best when the pressure is the greatest.

We know a clutch performance when we see it—Kirk Gibson's 1988 home run, Luis Gonzalez's 2001 bloop single, David Freese's '11 triple. And the first week of the postseason produced a highlight reel of them, from the Marlon Byrd home run in the NL wild card game that jump-started the Pirates to their first playoff win in 21 years, to David Ortiz's two homers in the Red Sox' ALDS Game 2 win over the Rays, to 28-year-old rookie catcher Stephen Vogt's bottom-of-the-ninth, game-winning single for the A's in Game 2 of their ALDS against the Tigers, to the stellar outings by two rookie pitchers: the Pirates' Gerrit Cole (the winner in Game 2 of the NLDS) and the Cardinals' Michael Wacha, who threw seven hitless innings against Pittsburgh in a Game 4 win.

There's no denying that clutch hits exist—but is there such a thing as a clutch hitter? The problem with answering the question is that reputations are often misleading. We think of Derek Jeter as Mr. Clutch because of a handful of memorable postseason hits—and one famous play in the field—but the numbers say that over his career he's been a slightly worse hitter in high-leverage situations, with an OPS of .825, than he is overall (.828). In late-and-close situations (plate appearances in the seventh inning or later, with your team tied, ahead by a run or with the tying run at least on deck) in the postseason, his numbers sink further (.751).

Similarly, we think of Ortiz as being born for the big moments—in 2005, Red Sox owner John Henry presented him with a plaque that read THE GREATEST CLUTCH HITTER IN THE HISTORY OF THE BOSTON RED SOX. But if you remove his 2000 and '05 seasons, Ortiz's lifetime clutch rating, as Nate Silver noted in a 2006 study, "is essentially zero." In 1,166 late-and-close plate appearances during the regular season Ortiz has a .373 on-base percentage and an .875 OPS, strong numbers to be sure, but below his overall career numbers (.381 OBP and .930 OPS).

Yet it is impossible not to be in awe of Ortiz's postseason heroics: In 52 career late-and-close PAs in October he has a .538 OBP and 1.282 OPS. The National League's answer to Ortiz as an October hero is Cardinals outfielder Carlos Beltran: His two home runs in the first four games of the NLDS against the Pirates brought his career postseason total to 16, moving him past Babe Ruth into eighth place on the alltime list. Beltran's postseason résumé is shorter than Ortiz's, but no less impressive. In 168 plate appearances he has a .464 OBP and a 1.247 OPS. Twenty-three of those trips have come in late-and-close spots. Too many Mets fans might better remember the outfielder for the called third strike he took against the Cardinals' Adam Wainwright to end Game 7 of the 2006 NLCS, but Beltran has a .522 OBP and a 1.522 OPS in those 23 plate appearances.

That good hitters are also good clutch hitters is not surprising. But it is worth noting that plenty of other great hitters seem to rise to another level in the clutch. Overall, Tigers third baseman Miguel Cabrera hit .348 with a 1.078 OPS this season, but those numbers jumped to .397 and 1.311 with runners in scoring position. "Miguel is a great hitter all the time, no matter the situation," says Detroit general manager Dave Dombrowski. "But with men in scoring position you just see the intensity. Can you measure this? Maybe not. But if you watch him on a daily basis, you see it."

So there is statistical evidence to suggest that clutch situations, in larger samples sizes, do bring out the best in some players—or in some teams. During the regular season the Cardinals hit .330 in 1,621 plate appearances with runners in scoring position, a mark that was not only well above the major league average of .255 but also the highest in baseball history, shattering the record held by the 1950 Red Sox (.312). St. Louis's home run total dropped by 21% from 2012, but the Cards improved their runs total from 765 to 783, tops in the NL. A key contributor to that increase was first baseman Allen Craig. Before a foot injury derailed his season in early September (he was left off the roster for the NLDS), Craig had a .454 batting average and .500 OBP in 152 plate appearances with runners in scoring position, well above his .267/.326 line in his other 411 PAs. Over the last 40 years only George Brett in 1980 and Tony Gwynn in 1997 have had a higher average with runners in scoring position.

Mabry says his team's success knocking in runners in scoring position was "a huge reason why we went as far as we did." So what are the 2013 Cardinals? One of the greatest clutch-hitting teams ever? Or just one of the luckiest?

IN ANALYTICAL circles clutch hitters are viewed largely as a myth—sabermetricians are more likely to acknowledge the existence of Sasquatch. Over the last 30 years hundreds of studies have been done on the topic, and not one proves that clutch hitters exists in any meaningful way—for the most part, players who come through in clutch situations one year do not replicate the feat in subsequent seasons. "Clutch hits exist, clutch hitters do not," says James Click, a former Baseball Prospectus writer and now the head of the Rays' analytics department, wrote in 2005. "There is no statistical evidence to support the idea that some hitters consistently perform better in situations defined as 'clutch' as compared to normal situations. Good hitters are good clutch hitters; bad hitters are bad clutch hitters."

But is it that simple? In his 2006 study Silver concluded that "clutch hitting ability exists more than previous research would indicate." And according to Tom Tango's extensive '07 study published in The Book: Playing the Percentages in Baseball, "About one in six players increases his inherent OBP skill by eight points or more in high-pressure situations; a comparable number of players decreases it by eight points or more."

Bill James dismissed the idea of clutch hitting as far back as 1984, when he wrote in his Baseball Abstract, "How is it that a player who possesses the reflexes and batting stroke and the knowledge and the experience to be a .262 hitter in other circumstances magically becomes a .300 hitter when the game is on the line? How does that happen? Until we can answer those questions, I see little point in talking about clutch ability." But even the godfather of baseball statistics has had second thoughts. James recently wrote that the discussion in the sabermetric community "has been fouled up for a long time," and that he no longer had faith in the data that had backed up the arguments against clutch hitting.

That statement sent shockwaves through the statistical community—to some, it was akin to a climate-change scientist suddenly denying global warming. James, however, was merely pointing out the difficulty in measuring clutchness with statistics because of the near impossibility of defining a clutch situation. James wasn't saying that clutch hitting doesn't exist. He was saying that it could exist. Nearly everything in baseball is now measured with staggering precision. Clutch hitting is one of the game's few remaining unknowns.

THE CARDINALS did not set out this spring to become the greatest clutch team in history. They did set out to improve their approach at the plate, after going 21--26 in one-run games in 2012—"Winning one-run games is all about situational hitting," says Mabry—and enduring long stretches in which the offense sputtered.

In the early days of spring training, the St. Louis coaching staff held situational hitting tournaments, assigning points to players for moving runners from second to third or for getting hits with the infield in. Every so often Mabry would have his hitters imagine how a postseason series in October could end: "Men on second and third—bring 'em home, and we win the pennant!"

The Cardinals don't see themselves as a clutch-hitting lineup, they see themselves as a lineup of disciplined hitters who control the strike zone and tailor their approaches to different situations. "Their approach is impressive," says Dombrowski. "You'd see them all the time getting the big hit, and where do they get most of their hits? The opposite field."

Indeed, much of what we think of as clutch hitting could be considered smart situational hitting. In Game 1 against the Rays, Boston's Jonny Gomes stepped to the plate after Tampa Bay rightfielder Wil Myers's misplay of an Ortiz fly ball put runners on second and third with one out. "Runner on third, less than two outs, that's something Jonny works on every day during BP," says Red Sox hitting coach Greg Colbrunn. "In those situations Jonny has a plan."

Gomes was a .247 hitter during the season, but with runners in scoring position he had a .346 average and a .543 slugging percentage. This time he lofted a high fly ball that scraped the Green Monster for a two-run double, sparking a Boston rally that turned a 2--0 deficit into a 5--2 lead. "You do have to change your swing [for] the situation," Gomes said later. "I was definitely looking to elevate the ball."

ANALYSTS ARGUE that professional ballplayers know how to deal with pressure, but anyone who's faced a 95-mph fastball with a championship on the line would tell you that some players look forward to big moments more than others.

Players deal with pressure situations in different ways. During Game 5 of the 1988 World Series, Dodgers righthander Orel Hershiser sat in the dugout between innings with eyes closed, his lips moving. "I was too excited about [winning the Series], so I relaxed and sang hymns," Hershiser, who nailed down a title with a complete-game win over the A's, explained. Gibson talks about how in the moments before his pinch-hit home run in Game 1 of that World Series, he quieted his mind by visualizing the entire moment. Says Reds second baseman Brandon Phillips, who hit only .223 in 107 late-and-close plate appearances, "In those clutch moments you do try to focus more. Honestly, I wish I could focus like that all the time. I'd be a beautiful hitter."

The clutch debate won't be settled this postseason. For one thing, it was the Pirates, not the historically-good Cardinals, who came up with the big hits in a series that went to a winner-take-all Game 5. In the first four games St. Louis went 3-for-21 (.143) with runners in scoring position.

Un-clutch or unlucky? A short series isn't a reliable litmus test for a the existence of the clutch effect—but then, little about baseball at this time of year is fair. A hit, you're a hero. An out, and you're the goat. That's the beauty and the cruelty of October.